1. Field of the Invention
The present invention relates generally to the field of manufacturing of optical fibers and particularly to the field coatings for optical fiber and the application of those coatings to the optical fiber.
2. Technical Background
Optical fiber (hereinafter xe2x80x9cfiberxe2x80x9d) has acquired an increasingly important role in the field of communications, frequently replacing existing copper wires. This trend has had a significant impact in the local area networks (i.e., for fiber-to-home uses), which has seen a vast increase in the usage of optical fibers. Further increases in the use of optical fibers in local loop telephone and cable TV service are expected, as local fiber networks are established to deliver ever greater volumes of information in the form of data, audio, and video signals to residential and commercial users. In addition, use of optical fibers in home and commercial business environments for internal data, voice, and video communications has begun and is expected to increase.
Fibers typically contain a glass core, a glass cladding, and at least two coatings, e.g., a primary (or inner) coating and a secondary (or outer) coating. The primary coating is applied directly to the glass fiber and, when cured, forms a soft, elastic, and compliant material which encapsulates the glass fiber. The primary coating serves as a buffer to cushion and protect the glass fiber core when the fiber is bent, cabled, or spooled. The secondary coating is applied over the primary coating and functions as a tough, protective outer layer that prevents damage to the glass fiber during processing and use.
In the process of manufacturing fiber, the length of fiber drawn from a preform is not the same as the length of fiber that is desired by an end users. In the case that the length of fiber is to short, the fiber may be spliced together to increase the length of the fiber. In splicing two lengths of fiber together, the coating is removed from one end section of two pieces of fiber. Each uncoated end of fiber is inserted into a splicing machine and the two end sections are fused together. Splicing apparatuses are commercial available to from such suppliers as Ericsson and Fujikura.
Problems associated with splicing together two fibers include how to protect the area where the protective coatings were removed from to perform the splice. These problems include what type of coating to use and how should the coating be applied and cured. The present invention addresses these deficiencies in the art.
One aspect of the invention relates to a coated optical fiber. The coated optical fiber includes a core surrounded by a cladding and a photopolymerizable coating applied to at least a segment of the cladding of the fiber, wherein the coating comprises at least about 60% of a first polyurethane acrylate coating composition having a Young""s modulus of at least about 400 MPa and about 5-40% of a second polyurethane acrylate coating composition having a Young""s modulus of no more than about 50 MPa.
Another aspect of the invention relates to a method of making a coated optical fiber. The method includes blending a coating composition mixture. The mixture comprises at least about 60% of a first polyurethane acrylate coating composition having a Young""s modulus of at least about 400 MPa and about 5-40% of a second polyurethane acrylate coating composition having a Young""s modulus of no more than about 50 MPa. The method further includes splicing an end section of a first optical fiber having a core and a cladding to an end section of a second optical fiber having a core and a cladding. The aforementioned mixture is applied to the end section of the first optical fiber and the end section of the second optical fiber and the coating mixture is cured.
The inventive composition has exhibited the advantage of having good adhesion to glass surfaces and also good adhesion to adjacent cured photopolymerizable coating material. Another advantage of the inventive coating is that the first polyurethane coating is infinitely soluble in the second polyurethane coating and vice versa.
A further advantage of the inventive coating is that the butt splice adhesion strength of the coating is substantially stable with respect to temperature. For example for splices formed at a temperature ranging from more than about 20xc2x0 C. to less than about 65xc2x0 C. the butt splice adhesion strength varied less than about 10%, more preferably less than about 5%, and most preferably less than about 3%, over the afore mentioned temperature range.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.